1. Field of the Invention
This invention relates generally to the electrometallurgical melting of titanium and titanium-based alloys. In particular, the invention relates to a method of magnetically-controllable, electroslag melting of titanium and multicomponent high-strength titanium-based alloys, and to an apparatus for carrying out the same.
This invention is useful in the production of titanium and high-alloy titanium alloys characterized by a high density of cast metal, an absence of gas pores and nonmetallic inclusions, and low contents of admixtures. The apparatuses and methods of the invention are particularly useful in the production of special-purpose alloys used for products that operate under conditions of long-term alternating loads, chemically aggressive media, and cryogenic temperatures, e.g., in aviation and shipbuilding industries, power generation and chemistry, nuclear power sector, etc.
2. Description of the Prior Art
Methods for the electroslag melting of metals discussed in Trochun I. et al., Magnetic Control of Crystallization in the Electroslag Process, Svarochnoe Proiz-vodstvo, 11:3-5 (1965).
The above study contains an analysis of the interaction between longitudinally-radial field and electric current, proceeding in a metallurgical pool. It has been demonstrated that such interactions result in bulk electromagnetic forces that affect the melt hydrodynamics and ingot crystallization. However, due to the unidirectional nature of vectors of melting current and the induction of external magnetic field in the course of titanium electrode melting, these forces may cause only an insignificant effect on the hydrodynamics of the melt, and thus exert little influence upon metal purification from admixtures and inclusions, leading to improvement of its macrostructures, microstructures, and quality.
The effect on electric current flowing in slag and metal pools, caused by the radial constituent of external magnetic fields, and resulting in more intense hydrody-namic motion of the melt is discussed in Paton B.E. et al., Development and Studies of Methods of Controlling the Structure of a Crystallizing Electroslag-Produced Ingot by Superposing a Magnetic Field, Problem Spetsialnoi Elektrometallurgii, 4:3-7 (1989). However, the melt rotation in the horizontal plane generated by electromagnetic forces, results in the formation of a crater in the central area of a metal pool, leading to the occurrence of a recess in this area, and therefore a negatively affected quality of ingot being melted.
Existing ESR methods are lacking in that they cannot provide metal homogeneity over the total length of the ingot. This is generally caused by the absence of mechanisms aimed at the stabilization of the ingot crystalline structure over the total length thereof by way of stabilizing the hydrodynamic situation in slag and metal melts.
This problem is most critical in the production of ingots made of high-strength, special-purpose alloys used for products that operate under conditions of complicated alternating loads and corrosion. When melting such alloys, it's highly desirable to differentiate the motion of melt in various areas thereof in terms of direction and intensity. Alloy elements used in these melts comprise heavy metals such as W, Mo, Fe, and Cr which must be uniformly distributed throughout the metal in the course of melting along with light alloy elements such as Al. Therefore, the more intense the melt motion, the more uniform the composition and the more uniform the composition of the crystallized ingot. Here, it is preferable to intensify such stream flows as well as to make the directions of their motion as complicated as possible. This will permit a more complete metallurgical process of dissolution of inclusions in the slag, thereby providing thermodynamic purification of the metal from gaseous admixtures and gas pores carried out by this slag.